Such aircraft oxygen emergency device are used to supply oxygen to passenger or cabin crew of an aircraft in an emergency situation like a decompression situation or smoke or generally reduced oxygen content or toxic content in the air inside an aircraft cabin. The oxygen emergency device must be capable of supplying oxygen to a single or a plurality of person immediately upon occurrence of such an emergency situation and over a time period which is sufficient to reach an airport and to evacuate the passenger.
Generally, a person will require a higher delivery rate of oxygen to be supplied in case of a decompression situation at a high flight altitude level than at a low flight altitude level. Thus, aircraft seek to descent in such a decompression situation in order to relieve the low pressure stress onto the passenger and to elongate the supply of oxygen. However, in specific situations, i.e. in case that mountains are to be passed such descent may not be possible.
Oxygen emergency devices are to be configured to supply oxygen in a sufficient delivery rate to a person for any flight level. It is known to store oxygen in a pressure tank to allow exact regulation and control of the delivery rate of the oxygen. However, such storage in a pressure tank has shown to be cost intensive as the sealing of such pressure tank must be under maintenance to always ensure the pressure tank to be filled completely. Still further, pressure tank have shown to add significant weight to such emergency oxygen systems.
A preferred way of storing oxygen is a chemical oxygen generator, wherein oxygen is stored in a chemically bound configuration and is produced in a chemical reaction upon a starting action like an ignition or the like. Such chemical oxygen generators can be designed to supply oxygen in different delivery rates but it is usually required to configure the chemical oxygen generators in such a way that a sufficient delivery rate is ensured for supply of oxygen to a passenger under conditions of a decompression event in a high flight altitude at a low temperature. Whereas in such specific emergency situation the chemical oxygen generator may provide exactly the delivery rate required by the passenger supplied with the oxygen a drawback of such configuration lies in the fact that far to much oxygen is generated in the chemical oxygen generator as soon as the aircraft has finalized its descent to continue on a low altitude flight level and/or a higher temperature in the cabin accelerates the chemical reaction. Thus, excess oxygen must be blown off in the environment and can not be consumed by the passenger and further increases the danger of feeding a fire within the cabin.
To overcome this drawback it is known from EP 2127699 A1 to provide an oxygen buffer for storing such excess oxygen generated in a chemical oxygen generator. The oxygen buffer is provided with oxygen via a spring biased check valve and can deliver the stored oxygen in a later phase of the process to elongate the supply time. A flow control valve is provided in the oxygen supply line to provide oxygen to the passenger at a predetermined pressure at a predetermined pressure level. This flow control valve is actuated by a control unit. Whereas this prior art arrangement has shown to significantly increase the time period during which oxygen can be supplied to a passenger the system at the same time increases the number of sealings and the weight of the whole emergency oxygen device. There is a need for more lightweight oxygen systems which however are capable of providing oxygen to a passenger for a long period of time at any flight level in a decompression situation.